Head-up displays (HUDs) are widely known to be used in vehicles as information providing means. Such Head-up displays can superimpose the foreground of a front visual field across a vehicle's window shield to display different sorts of driving information as virtual images (for example, speed display, navigation display, etc.).
Head-up displays cause virtual images to appear, for example, in a location about 3 m in front of the driver's seat. Techniques have been made public on how to make such virtual images appear in multiple locations (Japanese Patent No. 4941070, Jpn Pat. Appl. KOKAI Publication No. 2015-11212).